Treatment of cast iron



TATE

ifs

FFEQE noon 0. Anidernner, (Birdcage, mu, designers to Eilectro Metallurgical @ornuony, s2, commotion oi West Virginia,

No duplication September 3d, 1941,

em No. 4135MB s claims. (oi, vizise) T e invention relates to the manufacture of c st iron and provides s, new end useful method e, of treatment whereby the properties of the iron are improved.

A disadvantage of cost iron which has limited its use in the past is its wall-sensitivity, that is, sensitivity to variations in wall thickness or rate of cooling. An effect oi this well-sensitivity is that on iron which is desirably soft in heavy sections is undesirably hard, or chilled, in light sections. Considerable attention has accordingly been directed toward decreasing the sensitivity of cast iron to variations in cooling rate. the espedients proposed to attain this end, nanny involve the eddition to e molten list-ii of cast iron of agents celled grenliitizers, which usually contain. elements which not only promote the formation of gi'sploitic carbon in iron but also combine avidly with oxygen.

The improvement obtained by the oddition to molten cast iron of o grepliitizer in on amount sufilcient substantially to elimineie sensitivity to changes in cooling rate in the iron is sometimes accompanied by the production of minute, some= times microscopic, subcutaneous voids or pin- .lioles in the iron. Such voids ore quite different from imperfections arising from improper casting procedure; on iron containing them is sold to have "pinhole porosity. Pinhole porosity is perticolarly troublesome neceuse it is not usually evident from surface inspection of e, costing.

In general, cast iron is broadly divided into two classes, herd iron and soft iron. Whether on iron of e given carbon content is hard or soi't depends in large measure upon its silicon content. Thus, on iron. containing about 3% carbon and 1% silicon is hard, whereas an iron containing about 3% carbon and 3% silicon is soft. A polished and etched specimen cl 2" M d iron a, mottled enpeersnce; o. similar s cirnen of e. soft lronlias'e 'groy sppesrsnce. Til irons are particularly sensitive to verlstions in cooling rate ere materially benefited by the edclitlozi oi e srephltirer before casting. Soft irons, while not so sensitive to verletions rate, are else benefited by the addition of a grepliitizer. Both types of iron develop pinhole porosity when cost alter a grophitizing agent has been added; emit iron are particularly susceptible to pinhole formation.

priucipel object oi invent oi decreasing" n tions in coolin,

o without develo A more a onject is the formation of pinhole porosity in the iron when it is cost.

. which is o method of treating molten cast iron comprising temporarily raising the oxygen content of the molten iron in conjunction with, and preferably just prior to or simultaneously with, the addition of a grspliitizer containing 9. small amount of aluminum and one or more strongly deoxidins grsphltic-csrbon promoting" elements. Suitably the oxygen content of the cast iron is raised by the addition to it of o readily reducible metallic oxide, prefersoly in the ladle or would forehesrth just before the iron is cost, and con veniently in edmixture with the grephitizing agent. Oxides which may be used include iron omde, niclsel oxide, manganese oxide, and chromium onide, preferably in finely divided iorro. l'i' iron. oxide is used, convenient sources are iron ore end mill scale.

Procticslly all of the grapliltners in common use for the treatment of cast iron contain olumi nurn either as an impurity or es en intentionally added element. It was at first believed that aluminum alone was responsible for the develop ment of pinhole porosity in cast iron, but it has been observed that the tendency of on iron to develop pinhole porosity is most pronounced when 2. grepliitizer containing aluminum with other highly effective deoziolizing elements is used. When emphltizers containing less effective deoxidizlng elements are used, the tendency toward pinhole formation in the treated iron is less. However, grephitizers of the letter type have less chill reducing power than graphitlzers containing more efiectlve deon'ldizers.

Typical grephitizers which are used for the treatment of molten cast iron include ierrosilicons, modified ierrosllicons containing about 8.25% to 10% aluminum with or Without about 0.5% to 18% of one or more or the metals cel= cium, zirconium, and manganese, ferrosllioons containing about 1% to celcium and 12% to 25% vanadium or titanium-i. or both, end culcluln silicon alloys. As before stated, practically oil of these graphitizers contain some slum: it is usually present in o proportion at least about 0.25%. Grophitizers are usually odded to molten iron in an amount suiilcieut to add about 0.1% to 1.5% silicon to the iron.

In eocordsnce with invention there is added to niolteu cost 2 u in conjunction with the odditior o? grants '3, such on olloy oi the alcove n'ientioned no, onygon in en amount between about and 5 times the amount To the second batch was added 0.5% silicon theoretically necessary to combine with all or the just before casting by means of a ladle, addition of aluminum in the graphitizer to form aluminum the graphitizer used in Example 1. The iron oxide (A1203). Because the tendency of an iron was then cast. As cast its ultimate tensile to develop pinhole porosity depends on the comstrength was 20,300 pounds per square inch, its position of the iron, the amount and composition Brinell hardness number 156. The depth of chili,

. oi the graph'itizer used, and melting conditions, was 0.06 inch, but there was considerable pinhole the amount or oxygen to be added in a specific porosity.

instancemust be determined empirically. Gen- The third batch was treated in they ladle just erally, the softer the iron being treated or'the before casting with sufllcient graphitizerto add more eiiective as a deoxidizer the graphitizer 0.5% silicon, the samegraphitizer being used but used, the more oxygen should be added. Ordimixed with iron are containing 70% l 'eoOs, the narily, when a soit iron is to be treated with a ratio of ore to g-raphitizer being 117. The iron complex graphitlzer containing strong deoxidizwas then cast. Its ultimate tensilestrength was ing elements, the addition of about to to 2 times 20,900 pounds per square inch, its Brinell hard the amount of omen theoretically required to ness number 156. The depth of chili was 0.08 combine with all or the aluminum in the graphinch, and there was no evidence 0! pinhole .poitiner will be suiilcient to inhibit the-formation rosityv o! pinhole porosity without detrimentally ai- Example 3.-A hard iron containing 3.4% car-.-

' testing the chill-reducing power oi the graphbon and 1.8% silicon was made in a cupola under tiller. commercial conditions and divided into three Tests oi the method of the invention have batches. The first batch was cast immediately. demonstrated its eiiectiveness in substantially It had a tensile strength 01 35,600 pounds per eliminating the formation oi pinhole porosity in square inch. its Brinell hardness number was cast irons even when suchlrons have been treat- 19B, depth of chili was 0.94 inch, and there was ed while molten with excessive amounts or graphno evidence or pinhole porosity. itiaers containing strongly deoxidizing elements. To the second batch 0.5% silicon was added. In suchtests several cast ironswere made. some by means of a ladle addition of the graphitizerv were given'a graphitizing treatment, some were used in Example 1 just before casting. As east given the treatment or the invention, and others so th ir n s treated had a t nsile stren 0i were given no treatment. Standard test speci- 34,200 pounds per square inch and aBrinell hardmens were cast from the irons and were tested ness number 01' 187, andthe depth of chili was .101 strensth. hardness, depth or chill and evi- 0.14 inch. There was considerable pinhole podence or pinhole porosity. In the following can rosity. V amples typical results obtained in such tests are The third batch was treated with graphitizer' set iorth: plus iron ore as the third batch in Example 2.

Example 1.--Three heats or a sort iron mm The iron so treated had a tensile strength of taining about 3.5% carbon, 3% silicon and 0.8% 36,400 pounds per q re in h and a-Brinell hardmanganeso were made in a high-frequency rurness number or 196. The depth or chill'was 0.13-

' naco. One heat was cast without ladle adrli- 40 inch, and there was no evidence oi pinhole potions, the ingredients'simply being melted torosity. other. This iron as cast had an ultimate ten- In the following table the data obtained from silestnnlth of 19,500 pounds per square inch and the tests described in Examples 1.2, and 3 are a Brineil hardness number or 184. The depth -recapitulated for comparison. In the table of chili measured-on a standard chill block was T. 8." means ultimate tensile strength andis 0.18 inch, and there was no evidence or pinhole measured in pounds per square inch. "B; H. N). porosi means Brineli hardness number.

a second heat was made in which 0.75% silicon was added just before casting by a ladle addition 5 cm 233 *7 Emma or an iron-silicon-sirconium-manganese alloy so containing 2.6% aluminum. This iron as cast a 7 had an ultimate tensile strength or 24,300 polmds a H. N- 9 3:}, Pin p mslty per square inch. and its Brinellhardness numbei' was 146. The depth or chill was one inch Ma and considerable pinhole porosity was evident. 19,500 1 4 0.13 None.

a third heat was made in which 0.75% silicon 331% {3% 33% $132 was added in the ladle by the use of the same deoxldizer used in the second heat but mixed 23,; {61% :2, 3;? ,23 with a finely-ground iron ore in the ratio or 1 Hana 2 156 0.08 None. p on t '1 p t of er -p izer by weight. The so fitlti. saeoo lac 0.0; Do ore contained F9203. This iron as cast had 844 187 M4 c nshi' nblan ultimate tensile strength of 26300 pounds per m ineh, and its Brinell hardness number v was The depth of cm was reduced m The results 01' these and other tests'demon- 0.06 inch, and there was no evidence of pinhole as rate that large additions of mum!" to molten'tast iron effectively reduce the sensitivity sam le a-s medium hard iron containing the when cast variation! in of 3.0% carbon and 2.1% silicon was made in a awn-n3 but that the mm may dwell? Pinhole eupola under commercial foundry conditions and Emmsltyx It is further that 11 the 0mm divided into three batches. The first batch was 70 mutant of the molten iron is raised temporarily Least immediately. As cast its ultimate tensile during the graphitizinl; treatm t y m s a strength was some pounds per square, inch, and metallic oxide with the graphitizer, the chill-re- V 7 its Brlnell hardness number was 1'79. The depth during power of the amphitizer is not seriously oi chill was 0.22 inch. There was no evidence oi detrimentally aflected, and, may even be im-' pinhole porosity. V proved, while the tendency of the iron to develop pinhole porosity is substantiolly eliminated. The method the invention accordingly makes possible heavy additions of graphitizers to molten cast without encountering the risk of developing; pinhole porosity in the treated iron when cest.

Ii it is inconvenient or undesirable for any reason to add metallic oxides to the grephitizer used, the method of the invention may be precticed by oxidizing the grephitizer itself. For example, the graphitizer may be heated to a tern perature of about 900 C. to 1000" C. in an oxidizing atmosphere for a time between about or minutes to 2 hours depending on the degree of oxidation desired.

In tests of this method of adding oxygen to molten iron samples of the same s'raphitizer used in Example 1 above were heated at 950 C. for 15 minutes, at 950 C. for 1 hour and at 1000 C. for 2 hours. The samples were calculated to have a total oxide content of 2.38%, 3.28%, and 4.16% respectively, after treatment. The oxidized grephitizers were then added, in an amount suiiicient to add about 0.5% silicon, to a molten iron containing about 3.56% carbon and 1.91% silicon. No pinhole porosity was developed in the iron so treated, whereas the same iron to which had been added a similar amount of unoxi graphitizer had numerous pinholes..

The depth of chill of the untreated iron wee 0.56 inch: it was reduced to 0.13 inch in the iron treated with unoxidized graphitizer, to 0.14 inch in the iron treated with sraphitizer containing 2.38% oxide. and to 0.1? inch in the iron treated with graphitizer containing 3.28% oxide. The

depth of chill in the iron treatedwith grephitiaer con 4.16% omde was 0.25 inch.

It will be apparent that the invention is not limited. to the several specific examples cited herein by way of illustration of its principles. For example, it may be used with other graphitizera than those particularly mentioned, and

other metallic oxides which are readily reducible in molten iron may be used to supply oiwgen. The oxides used, although preferably in finelydivided form, may be used in briquetted form.

, the oxygen content of "the molten Modifications such as these of the method tie- :icribedherein are within the scope of the inven= What is claimed is:

1. In the process of making cast iron which includes the step of adding to the molten cast iron a graphitizing agent comprising principally silicon and at least one strongly-deoxidizing grsphitizing element, and containing a small amount or aluminum, whereby the cast iron is made desirably less sensitive to changes in chillins rate but undesirably susceptible to pinhole porosity, the method of counteracting such susceptibilty to pinhole porosity without materially afiecting such sensitivity to sees in chilling rate, which comp adding to the molten cast iron, in admixture with the said graphitizing agent readily reducible metal-oxide material in an amount only sumcient to supply between onehalf and five times the amount of oxygen theoreticelly required to combine with said alumimom.

2. Method as clnimed in claim 1, wherein the metel-omde material is iron oxide and wherein said iron oxide is added in an amount sunicient to supply about one-half to twice the amount oi oxygen theoretically required to combine with all or said aluminum.

3. A method oi treating molten cast iron which comprises 1 to the molten iron e fer-resilicon conta at least about 0.25% aluminum and at least one strongly deoxidimng, graphiticcarbon promoting element, said ferrosilicon being edded in a quantity suficient to add about 0.1% to 1.5% silicon to the iron, and during the addition of said ierzosilioon temporarily raising iron by adding in eturo with seidferrcsilicon at least one readily reducible metallic nude in an amount only sumcient to supply about it to 5 times the amount of oxygen theoretically required to comblue with ell or the alum present in said ierrosilicon. 

